1. Field of the Invention
The present invention relates to a locking apparatus and loadboard assembly for use in a semiconductor device testing apparatus and, more particularly, to a locking apparatus and loadboard assembly that provide unrestricted access to the loadboard, place no limitations on the size of the loadboard, ensure the correct alignment of the loadboard and provide even pressure on spring-loaded contact pins for proper testing.
2. Description of the Related Art
Semiconductor device testing apparatuses test various types of semiconductor devices including integrated circuits. Integrated circuits are tested to ensure that they will function properly in the consumer domain. Because integrated circuits must be individually tested, it is desirable that a semiconductor device testing apparatus accurately test integrated circuits at a low manufacturing test cost.
During the fabrication process, integrated circuits are tested in wafer form and in packaged form. In wafer form, a probe card is used to establish a temporary electrical contact between the integrated circuit to be tested (known as the device-under-test or DUT) and the semiconductor device testing apparatus (known as automatic test equipment or ATE). After completion of testing in wafer form, the integrated circuit is packaged and tested. Testing in packaged form includes a performance board or loadboard as the interface between the DUT and the ATE. The loadboard is a multi-layer printed circuit board that is mounted directly on the ATE. The DUT is inserted into a socket on the loadboard to establish electrical contact for testing.
FIG. 1 illustrates a conventional ATE system for testing an integrated circuit in packaged form. A tester 1 generates test signals which are transmitted to a test head 2 through cables 3. The test head 2, as shown by the cut-away view, houses a plurality of printed circuit boards or pin cards 4. The test signals are transmitted from the pin cards 4 to contact pins or pogo pins 5. The contact pins are represented schematically in FIG. 1 by arrows. It should be noted that the number of contact pins is much greater than what is illustrated in FIG. 1 and that the various elements of the ATE system in FIG. 1 are not drawn to scale.
The pogo pins 5 are spring-loaded and press against the loadboard 7 to establish electrical contact for testing. The loadboard 7 is positioned for such contact by being directly placed on the top surface 6 of the test head 2, known as the test head chassis or Hifix. The loadboard 7 is in turn a mount for socket 8. The DUT 9 in packaged form is inserted into socket 8 to establish electrical contact for testing. Thus, the test signals are transmitted from the tester 1 to the DUT 9 through the pin cards 4, contact pins 5, loadboard 7 and socket 8. The resulting signals from the DUT 9 are received by the tester 1 for evaluation through the same elements.
During testing, it is necessary to tightly secure the loadboard 7 to prevent any movement of the ATE from affecting the electrical contacts. This is typically achieved by a locking mechanism. The conventional locking mechanisms include a fixed slot with clamping to secure the loadboard and electrically or pneumatically controlled mechanisms to hold the loadboard in its position. FIG. 1 illustrates a portion of a conventional locking mechanism. The cut-away view shows a section of a securing structure 10 that keeps the loadboard in place.
FIG. 2 illustrates a close-up view of the top surface of a test head for a conventional ATE. Two identical loadboards 11 without any mounted sockets are shown on only a portion of the top surface 12. Each loadboard 11 is placed, secured and locked to the top surface 12 such that its sides are completely covered and its top surface is partially covered by the securing structure 13. Specifically, the securing structure 13 has four walls 13a 13b 13c 13d that surround the loadboard 11 on its four sides. The securing structure also has a top face 13e that partially covers the top surface of the loadboard 11. When the loadboard 11 is secured to the top surface 12 by bolts 14, the loadboard 11 is contained on its four sides and its top surface by the securing structure 13 thereby limiting the size of the loadboard and restricting access to it.
Loadboard size and access are important criterion for integrated circuit testing in a mass manufacturing environment. A large size loadboard allows for testing of multiple DUTs in parallel, thereby providing significant savings in manufacturing test cost. Unrestricted access provides further significant savings by reducing access time and maintenance and repair time. In view of the importance of size and access to lowering manufacturing test cost, the limitations on size and the restrictions on access placed by conventional locking mechanisms on loadboards such as in FIG. 2 preclude lowering manufacturing test cost.
Aside from the loadboard size and access, loadboard orientation is another factor affecting manufacturing test cost. When a loadboard is placed on the top surface of the test head, it must be oriented correctly for proper testing. Determining the correct orientation without orientation aids can be time consuming, and an improperly oriented loadboard on the top surface can be costly to correct. The loadboard 11 in FIG. 2 was placed on the top surface 12 without any orientation aids to ensure correct alignment. The absence of such orientation aids to guarantee correct alignment is another drawback of conventional locking mechanisms such as in FIG. 2.
Another factor affecting manufacturing test cost is the quality of the contact between the contact pins and the loadboard. The contact pins are spring-loaded and press against the loadboard to establish electrical contact for testing. If the loadboard does not provide even pressure on the contact pins, some contact pins may not properly press the loadboard for testing. Conventional ATEs use electric or pneumatic controlled levers to hold the loadboard in its position. However, these mechanisms are expensive and costly to maintain and repair.
It is an object of the present invention to provide a locking apparatus and loadboard assembly that overcome the above limitations of conventional locking mechanisms. The locking apparatus and loadboard assembly of the present invention provide unrestricted access to the loadboard, do not limit the size of the loadboard, ensure correct orientation of the loadboard and provide even pressure between the loadboard and the contact pins for proper testing. Furthermore, the locking apparatus and loadboard assembly can be manufactured independently at low cost.
In one embodiment of the present invention, the loadboard assembly includes a printed circuit board containing a device under test and an interface board secured to the bottom of the printed circuit board. This arrangement provides stiffness to the printed circuit board. It also allows for the entire top surface of the printed circuit board to be exposed, thereby eliminating any restrictions on size and access for the printed circuit board.
The loadboard assembly is then placed on top of a locking apparatus which is mounted on the top surface of a test head. The placement of the loadboard on the locking apparatus is done by aligning two pins of different cross-sections to extend through two holes in the interface board and printed circuit board of the loadboard assembly. This ensures that the loadboard assembly has the correct orientation for testing. Furthermore, by placing the loadboard assembly on top of the locking apparatus, access to the loadboard remains unrestricted and loadboard size remains unlimited.
When the loadboard assembly is placed on the locking mechanism, rollers mounted on the interface board are received in cam slots of a cam member of the locking apparatus. These rollers follow the grooves of the cam slots as the cam member is moved. Based on the shape of the cam slots, the loadboard assembly can be gradually lowered to achieve contact between the printed circuit board and the contact pins on the test head and to lock the interface board. In this manner, even pressure is applied to the contact pins to ensure proper testing.